To estimate expenses, consider setting aside a percentage for management fees, plus costs for cleaning and utilities.

I'm not sure why one would choose to make an (active) investment that is break-even, when there are other (passive) opportunities for RE ownership that can produce cash flows - i.e. private equity/syndications. 

these can produce good returns but best chance for success is for those that have experience in this area (I am a partner on an effort adding 8 ADUs, but it is not performing to the initial underwriting (underperforming) and it is an experienced team).good luck I get it, but not everyone has the opportunity of scale and building multiple units.

I also utilize BP calculators through my professional account to underwrite deals.

then, there are holding costs while you rehab - servicing the loan, insurance, utilities, the rehab. 

All utilities are split and are paid individually by the tenants.

For $500K go buy another income producing asset to offset any losses you might have.

A lot of lenders used to apply 35% for expenses, but in the last several years, the numbers for supplies, labor, utilities, taxes, etc… have increased significantly.Also take into account the age, occupancy and how has the property been maintained, this will affect the expenses too

Told them to do a drive by and call me back with an offer :)The person who called you probably just spent $15,000 for mentoring and “education”, and is now in panic that his 250 cold calls have not produced anything .  

Hi Tom, Building a manufactured duplex on land could offer great returns, but it comes with complexity—zoning, utility hookups, and permitting can delay your timeline and add hidden costs.